"Alone, a Legionary is a formidable foe as far beyond a man as the wolf is beyond the sheep. Together, bound by ties of unshakeable loyalty, a Legion is a force that can extinguish the stars and shake the very heavens."

The Space Marine Legions (also known as the Legiones Astartes) were the original unit formations of the Space Marines created during the First Founding by the Emperor of Mankind on Terra in the late 30th Millennium. This initial Founding happened before the start of the Great Crusade that reunited the scattered worlds of humanity beneath the banner of the Imperium of Man, while the Unification Wars were still raging on Terra. At the start of the Crusade, as the Legions were placed at the forefront of the Imperial Expeditionary Fleets that left Terra to reunite the human-settled galaxy, the Astartes were renamed Space Marines and their formations the Space Marine Legions. Unlike the current Adeptus Astartes, who serve the Imperium today as a planetary assault and rapid strike force, the Space Marine Legions were the primary frontline military forces of the ancient Imperium of Man. This role changed after the Second Founding, when the Imperial Guard replaced the Legiones Astartes as the Imperium's frontline armed forces, relegating the much smaller Space Marine Chapters to a more specialised role.

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Legiones Astartes

A Space Marine Legion was a frontline force of shock-infantry comprising tens of thousands of Astartes warriors armed and equipped with the finest wargear the Imperium could supply. A Space Marine Legion, unlike the 1,000-man Chapters of the present-day Adeptus Astartes created after the Second Founding at the end of the Horus Heresy, could number anywhere from 10,000 to more than 250,000 Space Marines, as well as the Legion's associated Imperial Army, logistical support forces and fleet elements. A force of a hundred of these genetically and biochemically-enhanced super warriors could quell a rebellious city in hours. Thousands could conquer worlds in days, and tens of thousands and even hundreds of thousands wielded at once were the doom of entire species, capable of reducing entire civilisations to mere dust and memory in a span no greater than the single course of Terra's orbit around the Sun.

Founded amid the bloodshed of the Unification Wars of Terra that swept the Emperor of Mankind to dominion over the cradle of humanity, the original military formation of the Legions was the division of twenty numbered units of enhanced warriors, organised very much along the lines of the Thunder Regiments that proceeded them in the Emperor's service and who they would eventually entirely replace. Much of the discipline and organisation of the early Astartes Legions owed greatly to the ancient and proven Terran patterns of strategy, hierarchy and functions as laid down in the revered texts of the Principia Belicosa of Roma and Krom's fragmentary New Model that had survived in the hands of the tyrants of Old Earth down the blood-stained generations of the Age of Strife. To these venerable treatises the Emperor and his commanders had added their own genius and created a sturdy but adaptable strategic framework that spoke to the fundamental strengths and superhuman abilities of the Legionaries themselves. At the outset of the Great Crusade in circa 800.M30, many of these early Legions were organised along the so-called "Terran Pattern" of organisation as formulated by the Imperial Officio Militaris.

Of the twenty original Space Marine Legions, eighteen would survive to grow into vast forces by the end of the Great Crusade in the early 31st Millennium; as for those that did not (the II and XI Legions), nothing can be said in current Imperial records. Nine of these Legions would continue to stay utterly loyal and faithful to the Emperor of Mankind during the Horus Heresy and thus they serve as the genetic forbears of all current Loyalist Space MarineChapters in the present era. The Space Marine Legions and their Primarchs were the Emperor's primary military forces and most important advisers, respectively, and were intended to be the political and military speartip of the Great Crusade. However, the Emperor also wanted to create a civilian government for the Imperium of Man which would ultimately hold authority over even the Primarchs, a change embodied in the creation of the Council of Terra in the early 31st Millennium that angered many of the Emperor's sons and ultimately became one of the contributing factors to the outbreak of the Horus Heresy. The Legions were aided by the ground and naval forces of the Imperial Army, the predecessor of the present-day Imperial Guard and Imperial Navy, but these forces more often served in support and garrison duties while the heaviest combat and the most important and difficult missions were always carried out by the Astartes Legions.

As the Great Crusade continued the expansion of the nascent Imperium into the galaxy, the discovery of the Primarchs and their newly adopted homeworlds helped to stem an impending crisis that was not widely known of at the time outside of the exalted ranks of the Imperium's ruling War Council: namely, the diminishing stability of the gene-seed itself through over-use and the increasing need for ever greater numbers of Space Marines in the field. This was a matter that only worsened as the Great Crusade pushed ever wider afield into the galaxy. Imperial forces could no longer be concentrated as easily as before, and attrition was taking its toll as years of near-constant battle became decades. To slow the relentless pace of the Great Crusade's progress was for the Emperor simply not an option, and so, the simple truth was that more Space Marines were needed and they needed to be created faster than before.

A secret conclave of gene-wrights under the Emperor's direct supervision posited the solution that became known as Grabiya's Theorem, which demonstrated that a Primarch's genetic code could be used to stabilise and expand Astartes gene-seed stocks with what was hoped to be "minimal deviation." Alongside this accelerated gene-culturing technique, other previously unavailable genetic technologies were put into effect, reducing the processing time required to create a battle-worthy Space Marine to a single Terran year in some cases. Such accelerated gene-seed techniques, along with absent, inadequate or over-forceful psycho-doctrination techniques, were later found to have unseen fundamental flaws. Many Imperial savants since have come to believe that the drive to create larger Space Marine Legions at accelerated speed played a prime role in the degradation of the sanity and psychological make-up of certain Legions and paved the way for the horror that was to come.

Nine of the twenty original Space Marine Legions chose to follow the WarmasterHorus and pledge their lives and service to Chaos. They became the Traitor Legions of Chaos Space Marines that still threaten the Imperium today. In the end, the Horus Heresy made clear that no single commander could be trusted to wield the enormous power of a Space Marine Legion, never mind several at once. The Ultramarines' PrimarchRoboute Guilliman led the Post-Heresy Reformation of the Imperium (the so-called Imperium Secundus) that reshaped the Space Marine Legions into the Adeptus Astartes and broke up each of the remaining Loyalist Space Marine Legions into the myriad 1,000-man Space MarineChapters to protect humanity from the rise of another Horus.

The remaining two Legions and their Primarchs were lost to the Imperium sometime before the Horus Heresy, with no trace of them remaining. It has been suggested that they were destroyed by, or under direct order, of the Emperor for some unknown, grave transgression, or flaw in their gene-stock, and all evidence of their existence purged from Imperial records.

Legion Size

The Legions were massive armies, and the size of each could vary tremendously. A precise, pre-set formation was never truly achieved or maintained. Even during the Great Crusade some Legions were very large, while others were not. The size of each Legion was fluid, with the numbers of combat-ready Astartes dependent on the number of new recruits, the inevitable battle-losses, the availability of potential recruits, and the administrative skills of the Primarch and his officers.

The largest of all the Space Marine Legions were the Ultramarines, followed by the Word Bearers. The Ultramarines numbered approximately 250,000 Astartes at their peak before the Battle of Calth and the Word Bearers numbered approximately 100,000. It was the Ultramarines' sheer size, as well as the purity of their gene-seed, which insured that more Second Founding Successor Chapters were created from the XIII Legion than from any of the other Loyalist Legions.

The Thousand Sons Legion of Magnus the Red was most likely the smallest of the Astartes Legions as many of the Space Marines within its ranks had developed rampant mutations or uncontrollable levels of psychic powers and had to be granted the Emperor's Peace. The Primarch Fulgrim's gene-samples had been largely lost on Terra making it difficult to develop new gene-seed for his Legion, and this meant that the Emperor's Children found it difficult to recruit new Astartes, also leaving it with a relatively small number of Space Marines. Both of these Legions would increase their numbers to acceptable standards only after their Primarchs were found by the Emperor during the course of the Great Crusade.

The approximate manpower available to several of the Space Marine Legions at the start of the Horus Heresy in the early 31st Millennium is recorded as follows:

Exact figures for the martial strength of the Alpha Legion at the outset of the wars of the Horus Heresy are impossible to obtain. Sources and estimates vary wildly, some making extravagant claims which may both overestimate or undervalue the Alpha Legion's manpower. Most contemporaneous account around the time of the Dropsite Massacre put the Alpha Legion at between 120,000 and 130,000 Legionaries strong, placing it within the middle tier of Legion strengths. Some theorists have pointed the figure as far lower, somewhere in the 90,000 range based upon the largest concentration of Alpha Legion forces ever seen in operation in a single theatre. With hindsight and diligent corroboration however, evidence of multiple simultaneous battle-groups operating in far distant locales suggests a far higher figure than either of these estimates, well into the range of 180,000 Legionnaires which, if accurate, would make it one of the most formidable Legions in sheer size alone, a factor unguessed by both sides of the war that was to follow.

At the time of the outbreak of the Horus Heresy, the Iron Warriors Legion is estimated to have had an active strength of between 150,000 and 180,000 Legiones Astartes, along with a very substantial war fleet of over a hundred Capital class vessels. More accurate assessment than this is, however, impossible given the considerable portion of sub-deployments and garrisons that were maintained by the Legion scattered across the Imperium and its increasingly isolationist tendencies in the years before the war. It is believed that the Legion had further accelerated its indoctrination and recruiting program, as well as local shipbuilding at Olympia in the lead up to the rebellion, and so the lower division of these estimates may indeed be erroneous.

130,000-170,000 Astartes during the latter days of the Great Crusade; approximately 70,000-110,000 Astartes following the losses sustained during the Istvaan III Atrocity. Heavily engaged on the surface of Istvaan III, it is estimated that some 30,000 of the Sons of Horus were dead or unaccounted for in the aftermath of that battle.

150,000 Astartes estimated at the XII Legion's peak. It is commonly estimated that of all the Legions that had fought at Istvaan III in the purge of the Loyalist faction within their ranks, it had been the World Eaters who had suffered the greatest casualties, with well over 35,000 World Eaters Legionaries believed to have met their deaths on both sides. Aside from the many wounded, it is recorded that a number had succumbed entirely during the protracted fighting to an insane bloodlust and had to be forcibly restrained and removed back to the World Eaters fleet for containment.

Exact numbers unknown; approximately 140,000 at the time of the Drop Site Massacre, though following their rebukement at Khur, the XVII Legion had grown to far greater strength then was originally reported.

In excess of 113,000 Astartes at the start of the Horus Heresy. Following the disaster of the Drop Site Massacre on Istvaan V, the X Legion was reduced to a mere shadow of its former strength. Exact estimates are unknown.

110,000 Astartes during the latter days of the Great Crusade; approximately 50,000 Traitor Astartes survived the Istvaan III Atrocity. No reliable account exists of the fatalities suffered by the III Legion during the excision of its Loyalist elements on Istvaan III, but it is believed to have been proportionally very high.

The strength of the Imperial Fists was never large in numbers, though not small, their tallies of warriors during the Great Crusade never rose above 100,000. At the time of the withdrawal to Terra, the Legion records show that the Temple held the outset of its living warriors, although such a number cannot be taken as accurate. The vagaries of Warp travel, Astropathic communication and the volume of space across which the Great Crusade was fought means that all that is certain is that this tally is nothing but plausible estimation.

95,000 Astartes at its peak. With the conclusion of the bitter fighting on Istvaan III, it is estimated that the XIV Legion had been reduced by well over 25,000 casualties, counting both the stubborn Terran Loyalists, betrayed to their deaths in the ash-mantled ruins of Istvaan III's Choral City, and Mortarion's sons of Barbarus whose lives had been spent to purchase their demise.

Total number unknown; approximately 89,000 Astartes at the end of the Great Crusade. 83,000 Astartes deployed with their Primarch Vulkan to Istvaan V. During the Drop Site Massacre, the XVIII Legion suffered nearly a total loss, rated by some sources as high as 98% of the Legion's Space Marine personnel. However, other detachments such as the garrison maintained at Geryon Deep and the Castellan of Prometheus' forces were comprised of about 2,000 to 3,000 total Astartes, alongside the full intake of Salamanders Neophytes in training on Prometheus. There also were several line companies of the Salamanders Legion on detached deployment elsewhere at the time of the Drop Site Massacre, leaving the total number of the XVIII Legion's effectives after the Drop Site Massacre unknown.

When the Raven Guard committed to the Istvaan V drop, they did so in number approaching their full strength, just under 80,000 Astartes, with all assets, both surface and space borne, in attendance. The Raven Guard were to lose nearly 75,000 Legionaries during the betrayal known as the Istvaan V Drop Site Massacre, and by the end of the ninety-eight days that followed, could muster but a fraction of their former strength. Leaving aside these unknown numbers operating alone in the outer darkness, the Raven Guard barely numbered around 4,000 including those despatched to garrison Deliverance. For the first time in their glorious history the Raven Guard were truly laid low.

At the time of the Drop Site Massacre, the Night Lords were estimated to comprise slightly over 90,000 Astartes, though others put their number closer to 120,000. Following their campaign against the Dark Angels in the Thramas Sector, their number had dwindled to an estimated 10,000 Astartes which comprised the VIII Legion during the remainder of the Horus Heresy.

Estimates of the Legionary strength of the VI Legion at the time of the Great Crusade and the Horus Heresy are not currently available.

Legion Organisation

Strategic Disposition of a Space Marine Legion during the later Great Crusade

The smallest formation within the "Logos Terra Militia" and therefore within the early Space Marine Legions was the squad. This consisted of a group of Legionaries under the command of a non-commissioned officer with the rank of Sergeant. Squads varied widely in both size and specialisation, with the majority of the units ranging between 10 to 20 Space Marines. Conversely, very specialised squads such as reconnaissance units or those that might have suffered heavy casualties, might only consist of a handful of Space Marines in active service. The chain-of-command was simple and direct, and the Legions' officers, themselves mighty warriors, would lead their Astartes into battle personally as had long been the wont of the techno-barbarian tribes of Old Earth, and the battle would be taken always to their enemy because to defeat a foe was never enough for the Legiones Astartes, only the utter destruction of an enemy of the Emperor counted as a victory. This cold logic, coupled with their inhuman strength and bearing, and the sheer dread they inflicted on friend and enemy alike, was to give the Space Marines one of their earliest appellations, and perhaps their most appropriate -- "the Angels of Death." It would be a name they would earn time and time again.

Legion Integration and Development

The Legions of the Great Crusade were a fusion of dual natures. They were the product of the Emperor's conquest of Terra and the Sol System. Selected from Terran stock and moulded by the wars of the nascent Imperium, these Legions held a certain commonality of character. A sense of unity and an almost familial bond pervaded their ranks. Given that they were all of the first generation of Astartes, born of Terra, they shared the imprint of their genetic forging and warlike history, and it is no surprise that members of the Legions regarded each other as siblings, as brothers-in-arms. Training, indoctrination and the shared experience of battle reinforced this belief within the Legiones Astartes, encouraging the idea that they were a family born in the cradle of war. This bond of brotherhood would survive as the Imperium grew, but perhaps it was never as strong as it was when the Legions first conquered techno-barbarians under the Terran sun.

The second face of each Legion was that of the people and cultures which had flourished under different stars. As the war to unify Terra became a crusade to conquer the galaxy the Legions grew. Casualties had to be replaced, and as the wars grew in scale so too did the number of losses and the number of recruits that were needed to take the places of the fallen. Initially intakes were drawn from Luna, Saturn's stations, the Proximal worlds, and dozens of others of the near Segmentum Solar fed the Legions' needs for warrior stock. As this occurred the Terran foundations of each Legion became diluted but was never overwhelmed, for the warrior tribes and cultures of ancient Earth were many and their commitment to the Great Crusade resolute.

With the re-discovery of the Primarchs and in many cases newly adopted homeworlds used as Legion fiefs (most commonly the worlds upon which a Legion's new master had been found), this was to change the character of the Legions profoundly. Some alterations were superficial: a habit of speech, a change in close-quarter tactics, martial traditions and warranted additions to iconography and even language. But for others the change would prove dramatic, with entire paradigms of culture, tradition and even ideology overwriting what had come before, such as in what came to be known as the Space Wolves and Dark AngelsLegions. In many cases the stamp of the Legions and the will of the Primarchs on their recruits came to largely outweigh differences of birth or blood, but in other Legions such as the Luna Wolves and the Emperor's Children, a subtle divide would grow between those veterans who had been recruited into the ranks of the Astartes by the Emperor from Terra and those who had come into the Legion from their Primarch's homeworld. This rift would be one factor among many that would lead several of the First Founding Legions towards ultimate damnation.

By the middle years of the Great Crusade the ongoing effects of these shifts within the Legions had resulted in a wide disparity in culture and organisation between them. The outward sign of this was the development of distinct character which meant the original Terran military patterns they had adhered to at the outset of the Great Crusade had been largely abandoned or become so modified and diluted as to be in some cases unrecognisable. There were, of course, exceptions in whole or in part, such as could be found within the Ultramarines and Iron WarriorsLegions who built upon rather than abandoned what had gone before, as well as those such as the White Scars to who the strictures and precepts laid out by the Officio Militaris were no longer even notionally applied. There are those that have cited this increasing idiosyncrasy in hindsight as the seeds of division, of a sense of insularity and "otherness" growing between one Legion and another. This itself only fuelled rivalries and feuds that had begun to simmer beneath the surface of the Great Crusade, both between the Primarchs and their Legions, that would later be exploited by Horus and his heretical conspiracy, and lay them open to the introduction of the Davinite warrior lodge cult structures into those Legions he favoured. These warrior lodges were the avenue by which the stain of the Warp would taint those Legions that turned Traitor.

Legion Structure

By the time of the outbreak of inter-Legionary hostilities during the Istvaan III Atrocity, the command and organisational structure of a Space Marine Legion was often more a mirror of the character and preferences of its Primarch and its abiding culture than formal writ. While certain formations and features were common as an outgrowth of practical manners such as deployment and logistics, their organisation and use was far from standardised. During the Great Crusade there were numerous terms for the internal constituent units of a Space Marine Legion, from largest to smallest: Great Companies, Regiments, Chapters, Battalions, Cohorts, Demi-Chapters, Companies, Squads and Maniples. Most often, the practical reality of their disposition would vary still more as terminology used within different Legions for equivalent ranks and specialisations bore the mark of the Legion's character rather than the desires of the Imperium's central administrators for a common nomenclature. In some cases this discrepancy increased as local languages and dialects such as Fenrisian or Khal'd had come to replace Imperial Terran (the forerunner of High Gothic). With these caveats in mind, the Strategic Disposition of a Space Marine Legion chart above describes the broad and most common structural basis of an Astartes Legion (as well as some of the more commonly used terminology of rank) in the latter half of the Great Crusade.

Generic Space Marine Legion Order of Battle

By the time of the middle years of the Great Crusade, there was great variation in each Space Marine Legion's order of battle and size. However, in the most generalised sense, a Space Marine Legion was a force comprised of approximately 11 or more smaller sub-units known as Chapters, each subsequently further divided into a deep hierarchy of smaller sub-units led by officers whose rank terminology often differed from Legion to Legion. The order of battle presented here should be considered generic and to be superseded by the more specific structure and rank terminology of a given Legion, if such information is available within current Imperial records.

Legion Command:Primarch or Legion Master (if the Legion's Primarch had not been rediscovered)

Chapter I (Chapters were alternatively designated as Great Companies, Harrows, Millennials, etc.)

Originally each Chapter was composed of roughly 1,000 line Legionaries, but as the Legions grew, this number began to vary substantially by Legion, and also through the vicissitudes of war and the availability of replacement recruits

Company I (Companies were alternatively designated as Maniples, Bands, Brotherhoods, etc.)

Nominally Battalions numbered five companies, each of a hundred Legionaries -- Company I was composed of Veterans and other elite units, II, III and IV were line companies and the V Company was comprised entirely of specialist troops such as dedicated Assault, Outrider or Destroyer units. However, in practice many larger Legions regularly exceeded this number of companies, maintaining battalions with seven or ten companies each folded under a particular command, while individual companies also varied in strength

Lieutenants were the most junior officers of the Legion. They also differed in designations such as Dominar, Decurion, Pack Leader or Chieftain, and in some Legions the numerical positioning of the officer within the Company indicated seniority or ceremonial role and had further titles in rank

Nominally each battalion was composed of five hundred line Legionaries each, as well as various specialists and support staff

Chapter IX

Chapter X

Chapter XI (etc.)

Original Legion Names

The Astartes Legions were for a very long time after their initial creation under the direct command of the Emperor and originally all Astartes recruits were drawn from Terra itself rather than the later Legion homeworlds of the Primarchs. The Terran Space Marines would always remember these early times before their Primarchs were re-discovered and the Legions initially had overwhelmingly Terran cultural traditions and origins. Later, as the Primarchs were found, the new recruits would have very strong loyalties towards them, and some of the Primarchs would re-name their Legions to accord with their own personalities and cultural sensibilities. The Emperor saw no problems with this development; he believed the loyalty of the Primarchs to him was unshakable. This reasoning would be proven to be sadly mistaken; for all their seeming physical and mental perfection they were still human beings and prone to all the sins of humanity, including greed, anger and the lust for power, recognition and advancement -- all emotions that left them susceptible to the temptations offered by the Ruinous Powers of Chaos.

The first Primarch to be found was Horus, rediscovered on the world of Cthonia. He was the Emperor's favorite, and he and his XVI Legion, the Luna Wolves, were granted the honour of being renamed the Sons of Horus following Horus' elevation to the rank of Warmaster, and his survival despite the wound that had nearly killed him on the moon of Davin. The I Legion was given the name Dark Angels by Lion El'Jonson, and the XIV Legion, the Dusk Raiders, had their moniker changed to the Death Guard by Mortarion. While its original name is unknown, the highly honorific name Emperor's Children was awarded by the Emperor to the III Legion only after a speech made by their Primarch Fulgrim so impressed the Emperor of Mankind that he granted that moniker to Fulgrim's Legion. The XII Legion was originally known as the War Hounds by the Emperor before the Primarch Angron renamed them the World Eaters. The XVII Legion, the Imperial Heralds, were renamed the Word Bearers after they were reunited with their highly religious Primarch Lorgar, who tragically intended to bring word of the Emperor's divinity to every world that his Legion brought into Imperial Compliance.

Body formerly possessed by a Greater Daemon of Slaanesh once contained within the Chaotic silver daemonsword Fulgrim found on the world of Laeran. Fulgrim achieved apotheosis and was transformed by the will of his patron deity into a Daemon Prince.

Lorgar achieved apotheosis and was transformed into a Daemon Prince of Chaos Undivided by the will of the Dark Gods; currently resides in "contemplation" upon the Word Bearers' Daemon World of Sicarus in self-imposed isolation, meditating within the Temple Inficioto as he seeks enlightenment and communion with the Ruinous Powers.

One of the twins may be dead, slain by Roboute Guilliman after the Horus Heresy. Both twins sided with Horus and were declared Traitor by the Imperium; however they considered themselves to be opposed to Chaos and their actions may simply be one more subterfuge amongst so many.